In the mass production of formed articles, such as thermoformed containers, bowls, plates, trays and the like, the counting and stacking of those articles is often performed manually. In those operations employing manual stacking, the article, after it is formed, usually passes into a receptacle or onto a conveyor where it is thereafter manually arranged into a stack. As can be appreciated, this often proves to be quite labor intensive, compared with the rest of the production operation. In such operations, excessive labor costs are often experienced, providing the motivation to develop mechanized stackers.
A variety of specialized stackers are known to those skilled in the art. For example, U.S. Pat. No. 2,782,942 discloses a stacking machine for the automatic stacking of round concave-convex articles, such as targets. The machine includes an elongated horizontally disposed frame, as article supply means in connection with the frame for the delivery of a continuous stream of articles and a plurality of like stacking mechanisms arranged in series lengthwise. The stacking mechanisms then deliver the stacked articles to a discharge means or conveyor.
U.S. Pat. No. 3,499,063 discloses an apparatus for collecting and stacking plastic articles received from a blow molding machine. The articles are stacked in a stacking frame which retains the stack by having the lowermost article rest on a spring loaded pawl which extends into the path of incoming articles at the opening. The incoming article moves into the opening, depresses the pawl, moves past the pawl and nests into the stack of articles, lifting the stack from the pawl in the process. Thereafter, the stack of articles is lowered back onto the pawl where it rests until the next article is inserted.
U.S. Pat. No. 3,765,546 describes an apparatus for the stacking of relatively heavy objects such as bins of fruit. The bins are supported by dogs which are pivotally mounted upon a pair of carriages positioned at each side of a conveyor. The carriages are slidably mounted upon upright posts and are arranged for joint vertical movement on the posts. Rack and pinion drive is provided to effect the requisite movement of the system disclosed.
U.S. Pat. No. 4,597,705 relates to an apparatus for the automatic stacking of a predetermined number of pie shells in nested relation for subsequent packaging. The automatic stacking machine disclosed includes an inverted U-shaped structure, the legs of which straddle a conveyor on which the items to be stacked are carried to a location between the legs of the stacker. The legs of the stacker house like means for engaging the item to be stacked on opposite sides and lifting the item to an elevated position where it is deposited on holding means to be retained while the lifting means is returned to the lower position for engaging and lifting the next item to be stacked. When the desired number of items are held in the stack, an automatic kicker means pushes the stacked items off the holding means and onto means for delivering the stack for further processing.
U.S. Pat. No. 4,802,808 discloses a stacking apparatus for deep-drawn plastic articles. The apparatus includes a removal station formed by a support plate forwardly moveable horizontally underneath the raised stack of formed articles, a pushing device arranged above the support plate and moveable parallel relative to the support plate, and a tilting frame located adjacent the support plate when the support plate is in the forwardly moved position.
Although the aforementioned devices have generally performed their intended stacking function in an acceptable manner, it is to be noted that the devices disclosed generally do not meet the needs which exist in the mass production of formed articles, such as thermoformed containers, bowls, plates, trays and the like. When thermoforming such articles, generally several articles will be formed transversely across a single web of thermoplastic material. The same thermoforming line will often be used to produce a wide variety of thermoplastic articles, with this flexibility arising from the fact that the molds employed can be easily changed out and replaced. As can be seen, for an article stacking and counting machine to achieve maximum utility in thermoforming operations, it must possess at least the same degree of flexibility vis-a-vis the types of articles it can be adapted to handle as that of the thermoformer. Moreover, it must be able to count and stack articles at a speed which is at least about equal to that of the thermoformer for it to operate as an in-line unit. Additionally, the easily crushed, flexible nature of the formed thermoplastic articles renders them easily destroyed in conventional machine stacking operations. None of the machines known in the art possess the type of utility required by the aforementioned forming operation.
Therefore what is needed is an apparatus and method for automatically counting and stacking formed articles which provides the speed, accuracy and flexibility required in the mass production of formed articles, such as thermoformed containers, bowls, plates, trays and the like.